Vitamin E refers to two groups of fat-soluble vitamins:

• Tocopherols—The more thoroughly studied form, as they were previously thought to be the exclusive source of vitamin E’s health benefits
• Tocotrienols—Current research is looking deeper into their health effects

Both tocopherols and tocotrienols have four forms: alpha, beta, gamma, and delta. All forms have unique properties, though their antioxidant effects in the body are their primary effects.

Tocopherol (with an –ol ending) is unesterified; tocopheryl (with a –yl ending) is esterified. Both forms appear to have the same functions in the body.

A common form of vitamin E sold in retail stores is “d-alpha-tocopherol,” which is considered the natural form. The synthetic form, "dl-alpha-tocopherol," is thought to be partially inactive (specifically, the L-portion).

Vitamin E is measured in International Units (IU). Specific amounts have been studied for different health conditions, but for general health, the FDA’s Daily Value for vitamin E intake is 30 IU. The Tolerable Upper Intake Level is set at 1,000 IU, due to animal and human studies suggesting that too much vitamin E may cause hemorrhaging and reduce the body’s blood clotting ability.

There has been much media attention regarding the Selenium and Vitamin E Cancer Prevention Trial (SELECT) findings, which found a higher incidence of prostate cancer in men supplementing with 400 IU per day of vitamin E. While further research is needed, it is generally recommended that men 55 and older supplementing with vitamin E or selenium do not exceed the Recommended Dietary Allowance for adult men of 22.4 IU per day.

Pure alpha-tocopherol can deplete gamma-tocopherol. Because recent research suggests that gamma-tocopherol has health benefits, mixed-tocopherol products (which contain both alpha- and gamma-tocopherol) may be preferable to alpha-tocopherol as a vitamin E supplement.